Probing the Low Surface Brightness Dwarf Galaxy Population of the Virgo Cluster

We have used public data from the Next Generation Virgo Survey (NGVS) to investigate the dwarf galaxy population of the Virgo cluster beyond what has previously been discovered. We initially mask and smooth the data, and then use the object detection algorithm Sextractor to make our initial dwarf galaxy selection. All candidates are then visually inspected to remove artefacts and duplicates. We derive Sextractor parameters to best select low surface brightness galaxies using g band central surface brightness values of 22.5 to 26.0 mag sq arc sec and exponential scale lengths of 3.0 - 10.0 arc sec to identify 443 cluster dwarf galaxies - 303 of which are new detections. These new detections have a surface density that decreases with radius from the cluster centre. We also apply our selection algorithm to 'background', non-cluster, fields and find zero detections. In combination, this leads us to believe that we have isolated a cluster dwarf galaxy population. The range of objects we are able to detect is limited because smaller scale sized galaxies are confused with the background, while larger galaxies are split into numerous smaller objects by the detection algorithm. Using data from previous surveys combined with our data, we find a faint end slope to the luminosity function of -1.35+/-0.03, which does not significantly differ to what has previously been found for the Virgo cluster, but is a little steeper than the slope for field galaxies. There is no evidence for a faint end slope steep enough to correspond with galaxy formation models, unless those models invoke either strong feedback processes or use warm dark matter.Comment: Accepted for publication in MNRA

New methods for B meson decay constants and form factors from lattice NRQCD

We determine the normalisation of scalar and pseudoscalar current operators made from non-relativistic $b$ quarks and Highly Improved Staggered light quarks in lattice Quantum Chromodynamics (QCD) through $\mathcal{O}(\alpha_s)$ and $\Lambda_{\text{QCD}}/m_b$. We use matrix elements of these operators to extract $B$ meson decay constants and form factors, then compare to those obtained using the standard vector and axial-vector operators. This provides a test of systematic errors in the lattice QCD determination of the $B$ meson decay constants and form factors. We provide a new value for the $B$ and $B_s$ meson decay constants from lattice QCD calculations on ensembles that include $u$, $d$, $s$ and $c$ quarks in the sea and those which have the $u/d$ quark mass going down to its physical value. Our results are $f_B=0.196(6)$ GeV, $f_{B_s}=0.236(7)$ GeV and $f_{B_s}/f_B =1.207(7)$, agreeing well with earlier results using the temporal axial current. By combining with these previous results, we provide updated values of $f_B=0.190(4)$ GeV, $f_{B_s}=0.229(5)$ GeV and $f_{B_s}/f_B = 1.206(5)$.Comment: 14 pages, 10 figure

Precision Charmonium Spectroscopy From Lattice QCD

We present results for Charmonium spectroscopy using Non-Relativistic QCD (NRQCD). For the NRQCD action the leading order spin-dependent and next to leading order spin-independent interactions have been included with tadpole-improved coefficients. We use multi-exponential fits to multiple correlation functions to extract ground and excited $S$ states. Splittings between the lowest $S$, $P$ and $D$ states are given and we have accurate values for the $S$ state hyperfine splitting and the $\chi_c$ fine structure. Agreement with experiment is good - the remaining systematic errors are discussed.Comment: 23 pages uuencoded latex file. Contains figures in late

Prospects for improved Λc\Lambda_c branching fractions

The experimental uncertainty on the branching fraction \b(\Lambda_c \to p K^- \pi^+) = (5.0 \pm 1.3)% has not decreased since 1998, despite a much larger data sample. Uncertainty in this quantity dominates that in many other quantities, including branching fractions of $\Lambda_c$ to other modes, branching fractions of $b$-flavored baryons, and fragmentation fractions of charmed and bottom quarks. Here we advocate a lattice QCD calculation of the form factors in $\Lambda_c \to \Lambda \ell^+ \nu_\ell$ (the case $\ell = e^+$ is simpler as the mass of the lepton can be neglected). Such a calculation would yield an absolute prediction for the rate for $\Lambda_c \to \Lambda \ell^+ \nu_\ell$. When combined with the $\Lambda_c$ lifetime, it could provide a calibration for an improved set of $\Lambda_c$ branching fractions as long as the accuracy exceeds about 25%.Comment: 8 pages, 2 figures, version to be published in Phys.\ Rev.\

Highly Ionised Gas as a Diagnostic of the Inner NLR

The spectra of AGN from the ultraviolet to the near infrared, exhibit emission lines covering a wide range of ionisation states, from neutral species such as [O I] 6300A, up to [Fe XIV] 5303A. Here we report on some recent studies of the properties of highly ionised lines (HILs), plus two case studies of individual objects. Future IFU observations at high spatial and good spectral resolution, will probe the excitation and kinematics of the gas in the zone between the extended NLR and unresolved BLR. Multi-component SED fitting can be used to link the source of photoionisation with the strengths and ratios of the HILs.Comment: Proceedings of the IAU Symposium: Co-evolution of Central Black Holes and Galaxie

Knowledge tree: Putting discourse into computer‐based learning

Most CBL materials currently in use model only the declarative aspects of the learning process. If such courseware is used without careful planning, this can be dangerous because one of the most fundamental aspects of education is the dialogue that occurs between teachers and the students. Traditionally, this has taken place in informal discussions as well as in formal small‐group learning sessions such as the conventional tutorial. However, as the student‐staff ratio increases, so does the opportunity for this type of personal dialogue decrease. Modern networking technology offers a huge potential to add discourse to CBL, but there are many pedagogical problems involved with the intrinsically ephemeral and anarchic nature both of the Internet and of most conferencing or bulletin‐board systems. In this paper we describe a software system called Knowledge Tree (KT) which we have developed to address some of these issues. KT combines a hierarchical concept‐oriented database functionality with that of a Usenet‐style bulletin board Using this, a knowledge garden may be developed for any subject area. These each contain a hypermedia database of frequently asked questions, together with answers provided by subject experts. There is provision for inter‐student discussions of problems and issues. When students ask new questions these are automatically emailed to a relevant subject expert (determined by a subject‐specific concept thesaurus). The answer is then placed in the database which eventually grows to become a valuable teaching resource. KT is discipline‐independent as the concept thesaurus can be changed to encapsulate any domain of knowledge. We have used it in support of conventional lecture courses, as an important component of a multimedia course, and for general IT support. These examples illustrate the role that this system can play both in basic information provision, and in facilitating the discussion of deep issues

D to K and D to pi semileptonic form factors from Lattice QCD

We present a very high statistics study of D and D_s semileptonic decay form factors on the lattice. We work with MILC N_f=2+1 lattices and use the Highly Improved Staggered Quark action (HISQ) for both the charm and the strange and light valence quarks. We use both scalar and vector currents to determine the form factors f_0(q^2) and f_+(q^2) for a range of D and D_s semileptonic decays, including D to pi and D to K. By using a phased boundary condition we are able to tune accurately to q^2=0 and explore the whole q^2 range allowed by kinematics. We can thus compare the shape in q^2 to that from experiment and extract the CKM matrix element |V_cs|. We show that the form factors are insensitive to the spectator quark: D to K and D_s to eta_s form factors are essentially the same, which is also true for D to pi and D_s to K within 5%. This has important implications when considering the corresponding B/B_s processes.Comment: To appear in the proceedings of The 5th International Workshop on Charm Physics (Charm 2012

Semi-leptonic decays heavy-light to heavy light

We present results for the QCD matrix elements involved in semi-leptonic decays of B-mesons into pseudo scalar heavy light states. The application of NRQCD heavy quarks allows for quark masses around the physical b-quark. We investigate the dependence of the form factors on the external momenta and looked at the mass dependence at zero recoil. For the first time, results for radially excited decay products are presented.Comment: 3 pages LaTeX, 5 figures, Talk given at LATTICE99(Heavy Quarks), June 29th to July 3rd, 1999, Pisa, Ital